Published: 20/04/26 By: Mike Bekin
In the battle of durability, there are ways to turn softer species into hardwearing, long-lasting timbers. The two industry heavyweights are thermo modification and preservative treatments, both of which can significantly improve durability and service life when correctly specified. But which process is better?
In this guide, we will compare thermo modification and preservative treatments, helping you find the best solution for your timber.
What is Thermo Modification?
Thermo modification subjects a less durable timber species (such as Pine, Frake and Ash) to high temperatures (typically 160–220°C) in a controlled, low-oxygen environment, with the super high heat changing the wood at a cellular level.
The timber which has been treated transforms into what we call ThermoWood, which absorbs significantly less moisture than the original timber species and enhances its resistance to decay. Now the timber is less likely to rot, swell, shrink and warp, creating a more stable and reliable product. Keep in mind that Thermo-modified timber is not suitable for ground or permanent water contact and must be correctly detailed and ventilated in external applications.
As a bonus, ThermoWood also takes on a deeper and richer colour than the original timber, with an aesthetic which is similar to many tropical hardwoods. For architects and designers, it is a perk which is hard to ignore.
ThermoWood at EcoChoice uses 100% FSC and PEFC-certified timber, making it a sustainable choice for your construction projects.
What Are Preservative Finishes?
Preservative treatments are applied to timber to protect against fungal decay, insect attack and rot. Rather than altering the timber’s cellular structure, they effectively create a barrier around the wood which enhances its durability for a longer-lasting timber product.
When carried out before installation, these preservatives can be impregnated deep into the timber for long-lasting protection which goes far beyond the surface. This is super handy if you plan on cutting the timber, ensuring that every new surface you create has the same level of durability.
ThermoWood vs. Preservatives
When it comes to choosing between ThermoWood and preservatives, there is a lot to consider. We have put together this handy chart to make weighing up your options a whole lot easier:
| Characteristic | ThermoWood | Preservative Treatments |
| Sustainability | Chemical-free, making it an eco-friendly choice which relies only on heat and pressure. | Some preservative treatments use biocides, and their environmental impact varies depending on formulation, retention level and end use. Make sure you choose an eco-friendly preservative to ensure sustainability. |
| Durability | Significantly enhanced resistance to decay and moisture thanks to permanent structural changes. | High durability as a result of deep chemical penetration which guards against rot, insects and fungus. |
| Dimensional stability | Very stable. Reduced moisture absorption means minimal swelling, shrinking or warping. | Moderately stable. Moisture resistance depends on the treatment type, but it does not alter the timber’s cell structure. |
| Maintenance requirements | Very low maintenance, with no need for multiple treatments. Simply treat with an oil or stain to maintain the colour of your timber. | Moderate maintenance. Some treated timbers benefit from periodic re-coating or retreatment, depending on the treatment used and your desired application. |
| Cost | Generally higher upfront cost, but often lower whole-life cost due to reduced maintenance | A cost-effective and widely available option. |
When to Use ThermoWood or Preservatives
Thermo modification and preservative treatments can both be great options, depending on the application of your timber.
In general, we recommend ThermoWood for exterior applications which you do not want to be constantly maintaining, such as external decking and cladding applications where ground contact is avoided and correct detailing is used. As a result of its enhanced structural integrity, it also makes a great option for interior joinery.
Preservative treatments are commonly used in both domestic and commercial projects, particularly where ground contact or high moisture exposure is expected, such as garden decking, fences and outdoor furniture. Just make sure to choose an eco-friendly finish for sustainable construction.
Buy Thermo-modified ThermoWood at EcoChoice
For a durable, sustainable timber, our top pick of the two will always be ThermoWood. The permanence of the treatment makes it much more reliable, and it boasts a longevity which is hard to beat. If you are won over by the wonder of ThermoWood, make sure to opt for a responsible supplier, such as EcoChoice. All our thermo-modified timber is sustainably sourced and either FSC or PEFC-certified, making it the best choice for your construction project and our planet.
Tags: thermally modified timber, treated softwood
Categories: Insights
